Checklist For Purchasing A Lens
I've been asked the question "What do you check for when buying a lens?" or "Is this a good lens?" more than once, and the question came up again today when a friend was buying a used lens.. So, I thought I'd share what I check for when buying a lens, new or old. Of course some of the items on the list are for zoom lenses only, but most can be attributed to lenses in general, zoom or prime.
1. Bring your camera body with you so that you can test the focus of the lens.
2. Inspect for dust and scratches on the lens surface and body. Chips and knicks aren't good especially if you plan to sell the lens as well one day. And of course you don't want dust and scratches in your shots, that will just increase post production time later.
3. Check for fungus or debris on the ring edges of the lens. Lens fungs is a BAD thing, you don't want to deal with that. I wouldn't advise buying a fungus infected lens regardless of the price. It only gets worse. Check out the length one photographer goes to avoid fungus.
4. Shake the lens, to make sure there are no loose elements, you should hear NO rattles (if you do, the lens has most likely been dropped or the person has used the lens a LOT zooming in and out) The damage done is normally the lens won't shoot as pin point as it did when it was newer because one of the elements isn't perfectly aligned anymore and the light isn't directed properly.
5. Check for loose switches as well.
6. Make sure the zoom ring and focus ring move smoothly throughout the focal length, and there are no areas where it "catches" or is hard to turn.
7. Hold the lens straight up, zoom at various focal lengths and ensure the weight of the lens doesn't close the lens back down a lot (this is called zoom creep, in cheaper lenses, this is common and unavoidable, it's just the build quality you get with cheaper lenses.) You can also do this holding the lens straight down. Open it slightly, and see if gravity opens the lens all the way or if it stays at the focal length you opened it to.
Then put the lens on your camera:
8. Check for is back focus or front focus issues.
(You'll have to use your LCD on the back of your camera for this)
Focus on something and then check the results in the LCD. If the lens focuses on the thing you expected it to, you're good. If it focuses on something in the foreground, you have front focus issues, if on something in the rear, back focus issues.
9. Focus on something far away and see how fast the lens autofocuses, then do the same for something close up. Do this at the short and long ends of the lens and ensure it's to your liking. In some photography, such as sports, you'll want a fast autofocus, and if the lens isn't quick, you could potentially lose a lot of shots. Also listen to the sound of the focus motor, is it too loud? You don't want to be obtrusive if shooting at a wedding with a loud focus motor.
10. Then I'd shoot at F4 to see how sharp the image is (that's normally the sweet spot for most lenses) It should be pretty sharp all the way to the edges
BONUS TIP: Ask for the box, and any warranty cards for the lens. Ask if there was a lens hood and make sure you get both lens caps (front and rear).
Hopefully this list will come in handy for you.. These are the things that I check for when I'm purchasing a lens. Don't let a slightly used lens scare you. You can easily determine if a lens is "LNIB" (Like New In Box) or "slightly used" as advertised by following this simple checklist. Don't be naive and think a new lens is perfect either.. Sometimes lenses can come defective from the factory, so don't be bashful, use this list on new lenses as well..
